Categorizing physically dissimilar stimuli such as objects, words, sounds, and other sensory events into the same class is fundamental to meaning, comprehension, and other aspects of cognitive development and functioning. This application studies fundamental learning processes that underlie stimulus-class formation and the resultant emergence of novel behavior, a characteristic of normal human development that is often deficient and in need of behavioral remediation in individuals with developmental disabilities. The broad objective is to demonstrate that even in the absence of language, establishing particular conditional relations between specific pairs of stimuli via reinforcement versus non-reinforcement yields sets of interchangeable stimuli (viz., stimulus classes) as evidenced by the subsequent ability to respond appropriately to novel, untrained combinations of those stimuli. The project aims are to show how such learning yields well-defined instances of emergent behavior rarely (if ever) seen in non-human animals, rigorously test the predictions of a model which assumes that ordinal position is coded as part of a stimulus' functional characteristics, and test the hypothesis that routinely non-reinforcing certain stimulus combinations while reinforcing other combinations generates stimulus classes containing the elements of the latter. In all of the proposed research, non-verbal animals possessing other, established categorization abilities (pigeons) will be concurrently trained on go/no-go matching tasks in which certain sequences of sample and comparison stimuli end in reinforcement whereas others do not. Later, stimulus-class formation will be tested by presenting novel sequences of those same stimuli. Besides revealing emergent effects, these tests will simultaneously evaluate the ordinal-specific properties of the hypothesized functional stimuli and the importance of continual exposure to non-reinforcement (as well as reinforcement) throughout training. Together, the expected pattern of findings will demonstrate that basic, general learning processes - in particular, the reinforcement contingencies used to establish conditional stimulus relations - can generate stimulus classes even in the absence of language and its neural structures and pathways.